Ka-Band Down-Converter with LTCC Technology for Satellite Communications

Abstract

KERAMIS-Geo is an R&D project funded by the German Space Agency DLR which aims at the development and verification of RF equipment for satellite communications in Ka-band. The basic and innovative technology development is based on LTCC (Low Temperature Co-fired Ceramic) modules with versatile RF functionality, robustness and hermetically sealed integration of MMICs. Within the project a 30 GHz to 20 GHz down-converter has been developed and was build up with 5 LTCC modules which have the following functionality: (1) Local Oscillator, (2) Frequency Control, (3) Mixer/Down Conversion, (4) Variable Gain Amplifier and (5) Driver Amplifier. Figure 1 shows the modules in the centre row of the Engineering Model (EM). All RF waveguide connections have been realized in a multilayer PTFE board in stripline technology which also include bandpass filters (BPF) and test ports to monitor the RF performance within the circuit. The DC and digital control unit is seen in the upper part of the photograph. This unique construction and technology is patent pending. The 20 GHz output port is shown on the left side of the unit realized with a coaxial connector, while the 30 GHz input port has been incorporated into the aluminum back-plate as rectangular waveguide transition from the LTCC substrate of Down Conversion Module. The bottom view of the down-converter is illustrated in figure 2. A 30 GHz waveguide-bend, isolator and adapter to coax-connector are mounted from the back side. A multipin connector for DC and digital control is visible in an opening of the back-plate. This Engineering Model is still in evaluation. The design of the Qualification Model (QM) will be finalized until the end of the KERAMIS-Geo project until end of September 2014. The consortium is aiming to continue the development and verification of the down-converter in a follow-up activity. Figure 3 shows the final housing and interfaces of the KERAMIS™ DOCON.

Full text

Ka-Band Down-Converter with LTCC Technology for Satellite Communications
Micro- and Millimetre Wave Technology and Techniques Workshop 2014
25-27 November 2014
ESA-ESTEC, Noordwijk, The Netherlands
Reinhard Kulke, Carsten Günner, Gregor Möllenbeck, Marcel Sohling, Jürgen Kassner
IMST GmbH
Carl-Friedrich-Gauss-Str. 2-4, 47475 Kamp-Lintfort, Germany
kulke@imst.de, guenner@imst.de, moellenbeck@imst.de, sohling@imst.de, kassner@imst.de
ABSTRACT
KERAMIS-GEO was an R&D project funded by the German Space Agency DLR which aimed at the development and
verification of RF equipment for satellite communications in Ka-band. Two devices were developed: a reconfigurable
switch matrix and a down-converter in Ka-band. This paper reports about the 30 GHz to 20 GHz down-converter unit.
The basic and innovative technology development is based on LTCC (Low Temperature Co-fired Ceramic) modules
with versatile RF functionality, robustness and hermetically sealed integration of MMICs. The down-converter consist
of 5 LTCC modules. Furthermore, all RF waveguide connections were realized in a multilayer PTFE board with
stripline technology as well as a DC and digital control board on multilayer FR4. This unique construction and
technology of integrating the LTCC modules is patent pending. The project ended with the evaluation of the
Engineering Model and the re-design for the Qualification Model. The consortium is aiming to continue the
development and verification of the down-converter in a follow-up activity.
INTRODUCTION
The KERAMIS-GEO consortium consists of various partners which cover specific disciplines for the development,
manufacturing and testing of such RF-devices for satellite communication. Those partners cover the entire development
and services chain. They are:
• OHB Systems (former Kayser-Threde) for system design and RF support
• IMST for RF-development and testing
• Micro Sytsems Engineering for LTCC manufacturing
• cicor RHe Microsystems for multilayer board technology and assembly
• Ilmenau Technical University for RF-design support
• Astro- und Feinwerktechnik Adlershof for housing analysis, manufacturing and tests
• STT-System Technik for DC/DC- and digital boards
• Airbus Defence and Space for customer tailored advice and support
The common R&D work from a core group of these organizations started in October 2003 with the project
KERAMISTM. Within this frame the basic circuits and modules were developed and tested in LTCC until September
2006. The results were promising and successful, so that the DLR funded the LTCC technology in a pursuing project
with the goal, to develop and qualify experimental circuits for the On-Orbit-Verification within the research satellite
platform TET-1 among 11 other scientific payloads. The KERAMIS-Box with three independent experimental circuits
for satellite communication was developed in the KERAMIS-2 project, [3] ... [10]. The payload could be delivered in
March 2011 for accommodation and was launched into space on a low-earth-orbit in July 2012 for 14 months operation
and verification. This was done in the frame of the OK-Tech project, [1] and [2]. During that period the partners
successfully collected and evaluated data from their circuits. The verification finally confirms the reliability and raises
the technology readiness level of the LTCC circuits to TRL = 9. This successful story encouraged the partners to apply
with this KERAMISTM technology for a GEO satellite mission. A challenging opportunity came up with the
announcement of the Heinrich-Hertz communication satellite. This German platform, organized by the DLR, is
intended for a commercial and a verification payload in Ka-band. The consortium applied for participation within the
project KERAMIS-GEO. Two devices as parts of the entire communication system were planed: a reconfigurable
switch matrix (RSM) and a down-converter (DOCON) for 30 GHz und 20 GHz signal conversion. The project started in

April 2011 and was finished in September 2014 with the evaluation of the Engineering Model and the design for the
Qualification Model. The RSM will probably be continued for the qualification of a Protoflight Model, while the further
development steps for the DOCON are not yet finally defined. However, it was decided not to participate in the
Heinrich-Hertz mission. There are still a couple of performance parameters and commercial issues to be solved before
finalizing a flight demonstrator. Nevertheless the development work will be continued. The next innovative step
towards a configurable down-converter will be the integration of a one-chip fractional-N synthesizer as local oscillator
source. This SiGe chip can be found under its project name NOVELO and is a development of IMST.
This paper will summarize the RF development and testing work of IMST as contribution to the KERAMIS-GEO
project. The focus lies on the Engineering Model and the improvement measures for the Qualification Model.
ENGINEERING MODEL OF DOWN-CONVERTER
Within the KERAMIS-GEO project a 30 GHz to 20 GHz down-converter (DOCON) has been developed and was build
up with 5 LTCC modules which have the following functionality: (1) Local Oscillator, (2) Frequency Control, (3)
Mixer/Down Conversion, (4) Variable Gain Amplifier and (5) Driver Amplifier with detector for output power. Fig. 1
shows these modules in the centre row of the Engineering Model (EM). All RF waveguide connections have been
realized in a multilayer PTFE board in stripline technology which also includes bandpass filters (BPF) and test ports to
monitor the RF performance within the circuit. The DC and digital control unit in multilayer FR4 is seen in the upper
part of the photograph. All LTCC modules are connected to the DC/control board from the upper side and to the RF
waveguides from the lower side using wire-bonding transitions. It ensures that the critical RF bonds can be realized as
short as possible. This unique configuration and technology is patent pending. The 20 GHz output port is shown on the
left side of the unit realized with a coaxial connector, while the 30 GHz input port has been incorporated into the
aluminum back-plate as rectangular waveguide transition from the LTCC substrate of Down Conversion Module (3).
Fig. 1. Down-converter circuit
The block-diagram of the down-converter is illustrated in Fig. 2. All MMICs were integrated in LTCC modules which
were hermetically sealed. Each LTCC tile consists of 6 ceramic layers including a cavity within the KOVAR frame.
Bare dies are mounted on the LTCC while RF and DC connections were realized with wire-bonds. Chip capacitors
around each MMIC ensure a reliable DC supply. Further RF structures are also integrated into the ceramic. Fig. 3 shows
photographs of open LTCC modules. The KOVAR frame was already mounted. Inside and outside of these frames RF
waveguides, transitions, couplers, filters as well as DC and control lines are visible. Some larger SMD components
were assembled out of the hermetic package. All RF ports in ground-signal-ground configuration are located at the
upper edge of the ceramic, while the DC connections are all designed at the opposite edge. The down-conversion
module (3) has a solid rectangular area in the corner. This is the place, where a stripline to waveguide transition was
realized.

Fig. 2. Block-diagram of down-converter
The bottom view of the EM DOCON is illustrated in Fig. 4. A 30 GHz waveguide-bend, isolator and adapter to coax-
connector are mounted from the back side. A multipin connector for DC and digital control is visible in an opening of
the back-plate. This EM is now evaluated. It shows the basic functions of down-conversion. DC supply and digital
control circuits work as developed. RF specifications could not be met over the entire frequency range. The target
specifications are summarized at the end of the paper. Test ports within the down-converter allowed to measure internal
RF parameters (see Fig. 1). Some measurements with RF probes could be made directly on the RF ports of the LTCC
modules before the wire-bonds were placed. This provided valuable data for re-design measures. Further attention of
the EM evaluation was drawn on technological issues. New assembly and integration processes were used. Critical parts
for the RF performance were identified like connector mounting or RF board manufacturing and assembly or isolator
integration. All issues were discussed with partners and were taken into account for the design and layout of the
Qualification Model (QM). The QM layout was finalized until the end of the KERAMIS-GEO project at the end of
September 2014. The consortium is aiming to continue the development and verification of the down-converter in a
follow-up activity.
Fig. 3. LTCC modules (open housing)

Fig. 4. EM: Bottom view of aluminium carrier with RF, DC and digital interfaces
Fig. 5 shows the final housing and interface concept of the KERAMIS™ DOCON. The RF part as described above will
be directly mounted on the inner plane of the sidewall, which is facing the observer. A waveguide transition is realized
by an opening in the sidewall followed by a rectangular waveguide bend and a waveguide isolator module. The housing
was designed with regard to all electrical, thermal and mechanical requirements for a GEO satellite mission. Multiple
DOCONs can be arranged in a row.
Fig. 5. PFM: DOCON housing with RF, DC, digital and mechanical interfaces
ACKNOWLEDGEMENTS
The authors wish to thank the project partners for long time and close cooperation within the frame of the KERAMIS
projects since 2003. The work described in this paper has been funded by the Federal Ministry of Economics and
Technology (BMWi) executed by Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) in the frame of the project
KERAMIS-GEO (funding code: 50 YB 1108).

TARGET SPECIFICATIONS FOR DOCON
Frequency Range (Uplink) 27.5 … 31.0 GHz
Frequency Range (Downlink) 17.2 … 21.7 GHz
Local Oscillator Frequency 9.8 GHz (adjustable)
Input Signal Bandwidth ≥ 500 MHz
RF Input Power Range -55 … -15 dBm
RF Input Return Loss ≥ 19 dB
IF Output Return Loss ≥ 15 dB
Overall Gain 11 dB
Max. RF Output Power 0 dBm
Power Consumption < 15W
Temperature Range (Operating) 0 to +55 °C
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